Aerogel-based mold for MEMS fabrication and formation thereof

ABSTRACT

The invention is directed to a patterned aerogel-based layer that serves as a mold for at least part of a microelectromechanical feature. The density of an aerogel is less than that of typical materials used in MEMS fabrication, such as poly-silicon, silicon oxide, single-crystal silicon, metals, metal alloys, and the like. Therefore, one may form structural features in an aerogel-based layer at rates significantly higher than the rates at which structural features can be formed in denser materials. The invention further includes a method of patterning an aerogel-based layer to produce such an aerogel-based mold. The invention further includes a method of fabricating a microelectromechanical feature using an aerogel-based mold. This method includes depositing a dense material layer directly onto the outline of at least part of a microelectromechanical feature that has been formed in the aerogel-based layer.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a divisional of U.S. application Ser. No.12/017,944, filed on Jan. 22, 2008, which is incorporated by referenceherein in its entirety.

FIELD OF THE INVENTION

The invention relates to an aerogel-based mold useful in the creation ofa microelectromechanical features. Further, the invention relates tomethods of forming an aerogel-based mold and methods of fabricating amicroelectromechanical feature using an aerogel-based mold.

BACKGROUND OF THE INVENTION

Microfabrication techniques used to generate structures inmicroelectromechanical systems (MEMS) generally involve directpatterning of the material layer into which a MEMS structure is formed.Methods used include photolithography, laser etching, plasma etching,focused ion-beam writing, electron-beam writing, and the like. Theseprocesses can consume immense time. Photolithography, for example,requires complicated masking procedures and precise control of theetching rates of various etchants. Other methods, such as focusedion-beam writing, laser etching, and electron-beam writing, largelyobviate the need for complex masking procedures. Nevertheless, usingthese techniques to direct-write a MEMS structure into a material layercan still require immense time because of the quantity of matter thatmust be ablated from the material layer.

SUMMARY OF THE INVENTION

Embodiments of the present invention are directed to materials andmethods that reduce the time required to form a patterned materiallayer, and thus reduce the time required to fabricate amicroelectromechanical feature.

A patterned aerogel-based layer serves as a mold for amicroelectromechanical feature. The density of the aerogel-basedmaterial is less than that of typical materials used in MEMSfabrication, such as poly-silicon, silicon oxide, single-crystalsilicon, metal, metal alloys, and the like. Therefore, one may formstructural features in the aerogel-based layer at rates significantlyhigher than the rates at which structural features can be formed indenser materials. This permits one to pattern an outline of amicroelectromechanical feature into the aerogel-based layer in much lesstime than would be required to pattern a similar microelectromechanicalfeature into denser materials.

The invention further includes a method of patterning an aerogel-basedlayer to produce such a mold. This method includes using techniques thatmay direct-write fine-scale device features, such asmicroelectromechanical features, into an aerogel-based layer.

The invention further includes a method of fabricating amicroelectromechanical feature using an aerogel-based mold. This methodincludes the deposition of a dense material layer directly onto anaerogel-based layer having a structural feature whose surface contour issubstantially the same as the surface contour of at least part of amicroelectromechanical feature. This results in a microelectromechanicalfeature whose structural stability and mechanical integrity aresufficient to permit a MEMS apparatus formed therefrom to function in ananalogous manner to a MEMS apparatus whose features are formed bydirect-writing into a dense material, such as silicon or silicon oxide.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 depicts an aerogel-based layer into which a MEMS-scale cavity hasbeen created.

FIG. 2 depicts the use of a focused ion beam to direct-write aMEMS-scale cavity directly into an aerogel layer.

FIG. 3 depicts a MEMS-scale cavity formed by depositing a dense materiallayer directly onto a patterned aerogel layer.

DETAILED DESCRIPTION

The following section describes the invention in further detail, andillustrates particular embodiments of the invention. This descriptionalso illustrates particular embodiments of the terms used in the claims.In both instances, these particular embodiments are offered forillustrative purposes, and are not to be used to limit the scope of theclaimed invention. This detailed description provides limitingdefinitions of several terms, which are identified by expressdefinitional language, i.e., “X is defined as Y.” Unless such expressdefinitional language appears in a description, the description ispresumed to be illustrative and non-limiting.

Unless expressly defined, all technical and scientific terms used hereinhave the same meaning as commonly understood by one of ordinary skill inthe art to which this invention belongs.

All publications, patent applications, patents, and other referencesmentioned herein, if not otherwise indicated, are explicitlyincorporated by reference herein in their entirety for all purposes asif fully set forth in the present specification.

Unless otherwise stated, all percentages, parts, ratios, etc., are byweight.

When an amount, concentration, or other parameter is given as a range,or a list of upper and lower values, this is to be understood asspecifically disclosing all ranges formed from any pair of any upper andlower range limits, regardless of whether ranges are separatelydisclosed. Where a range of numerical values is recited herein, unlessotherwise stated, the range is intended to include the endpointsthereof, and all integers and fractions within the range. It is notintended that the scope of the present invention be limited to thespecific values recited when defining a range.

When the term “about” is used in describing a value or an end-point of arange, the invention should be understood to include the specific valueor end-point referred to.

As used herein, the terms “comprises,” “comprising,” “includes,”“including,” “has,” “having,” or any other variation thereof, areintended to cover a non-exclusive inclusion. For example, a process,method, article, or apparatus that comprises a list of elements is notnecessarily limited to only those elements but can include otherelements not expressly listed or inherent to such process, method,article, or apparatus. Further, unless expressly stated to the contrary,“or” refers to an inclusive or and not to an exclusive or. For example,a condition “A or B” is satisfied by any one of the following: A is true(or present) and B is false (or not present); A is false (or notpresent) and B is true (or present); and both A and B are true (orpresent).

The use of “a” or “an” to describe the various elements and componentsherein is merely for convenience and to give a general sense of theinvention. This description should be read to include one or at leastone, and the singular also includes the plural unless it is obvious thatit is meant otherwise.

As used herein, the following terms are defined as follows. Thesedefinitions apply to the use of these terms within all portions of theapplication, including the claims.

An “aerogel” is defined as a low-density solid-state material resultingfrom the substantial removal of liquid from an alcogel withoutsubstantially damaging the solid part, such that the resulting solidretains at least about 50% of the volume of the alcogel. According tothis definition, an aerogel need not consist entirely of a singlechemical composition, such as a pure silicon oxide aerogel, but may alsoinclude combinations of multiple gel-forming compositions, such as asilicon titanium oxide aerogel, and the like. An aerogel may alsoinclude additives and/or impurities, as long as the presence of theadditives and/or impurities does not inhibit formation of an alcogel orinhibit the subsequent conversion of the alcogel into an aerogel.According to this definition, an aerogel need not have uniformcomposition throughout.

An “alcogel” is defined as a substantially rigid structure that resultswhen a sol substantially reaches its gel point. The sol comprisesreactants (typically, though not exclusively, metal oxides) that undergochemical reactions leading to the generation of species of continuouslyincreasing molecular weight. As these species increase in molecularweight, they link together so as to form a three-dimensional network. Ator near the gel point, the three-dimensional network substantially spansthe volume of the sol, so as to yield a substantially rigid structure,an alcogel.

An “aerogel-based material” is defined as a material comprising anaerogel, where a substantial portion of the gaseous volume of theaerogel remains unoccupied by other non-gaseous material. Anaerogel-based material, according to this definition, may includecomposites of an aerogel with other materials and/or compositions, solong as the other materials and/or compositions are present inquantities such that a substantial portion of the gaseous volume of theaerogel remains unoccupied by other non-gaseous material. Anaerogel-based material, as defined herein, need not be compositionallyuniform throughout, so long as a substantial portion of the gaseousvolume of the aerogel remains unoccupied by other non-gaseous material.

An “aerogel-based layer” is defined as a layer, or a sublayer or regionwithin a layer, substantially comprising an aerogel-based material.

A “substrate” is a material layer that underlies the material layer thatcomprises the aerogel-based layer, and provides structural support. Thematerial layer comprising the aerogel-based layer need not maintaindirect physical contact with the substrate. For example, interveninglayers or sublayers may or may not be present.

As used in reference to an aerogel-based layer, a “thickness” is definedas the distance between a top extension of the aerogel-based layer and abottom extension of the aerogel-based layer, as measured before theaerogel-based layer is subjected to writing, where the measurementoccurs on an axis perpendicular to the substrate.

As used herein, “writing” is defined as a single-step or multi-stepprocess which results in the net ablation of matter from one or morematerial layers. The invention is not limited to any particular ablationmethod except to exclude ablation methods that result in structuralfailure of the aerogel-based layer.

A “structural feature” is a feature resulting from writing into one ormore material layers.

As used herein, a “surface contour” is defined as the surface geometryof a feature in terms of the relative three-dimensional positioning ofthe surface characteristics of the feature. Therefore, when the surfacecontours of two features are compared (for example, to say that thesurface contour of one feature is substantially the same as the surfacecontour of another feature), this comparison is based only on therelative positioning of surface characteristics within each feature.Comparison of the surface contours of two or more features, thus,excludes all consideration of absolute size. As used herein, the phrasewill generally refer either to a surface contour of a structural featureformed, at least in part, by ablation of an aerogel layer, or to atleast a part of a micro electromechanical feature.

As used herein, a “microelectromechanical feature” is defined as afeature that forms at least a part of a mechanical, electromechanical,or opto-electromechanical apparatus, where the largest linear dimensionof the feature, drawn along any axis, is no longer than about 1 mm andno smaller than about 100 nm. The invention is not limited in scope toany particular type of apparatus, feature, or part thereof, so long asthe feature has the established size restrictions and is capable ofperforming a mechanical, electromechanical, or opto-electromechanicalfunction.

As used herein in reference to a dense material layer, “depositing” isdefined as a method of forming a layer of a material onto a surface. Theinvention is not limited to any particular technique for forming amaterial layer, except to exclude techniques that would result innon-trivial degradation of the aerogel-based layer or that would resultin the structural failure of the aerogel-based layer.

As used herein, “dense material layer” is defined as a material layerhaving no more than about 50% gas by volume. According to thisdefinition, the volume occupied by interstitial points in the crystalstructure are considered to be occupied by gas.

As used herein in reference to an aerogel-based layer, “removing” isdefined as a method of stripping away the aerogel-based material. Theinvention is not limited to any particular stripping technique, exceptto exclude techniques that would result in non-trivial degradation ofany dense material layer or layers deposited over the aerogel-basedlayer.

An aerogel-based layer may be formed on a substrate by any techniqueknown to those of skill in the art. The invention need not be limited bythe means in which the aerogel-based layer is formed. In one embodiment,the aerogel layer consists of a silicon oxide aerogel deposited onto asubstrate by methods disclosed in the following references: G. S. Kim &S. H. Hyun, Thin Solid Films, Vol. 460, pp. 190-200 (2004); S. S.Kistler, Nature, Vol. 127, p. 741 (1931); P. M. Norris & S. Shrinivasan,Ann. Rev. Heat Transfer, Vol. 14, pp. 385-408 (2005, V. Prasad, et al.,eds.); S. S. Prakash, et al., Nature, Vol. 374, pp. 439-43 (1995); K.Richter, et al., Ann. Rev. Heat Transfer, Vol. VI, pp. 61-114 (1996); L.W. Hrubesh & J. F. Poco, J. Non-Crystalline Solids, Vol. 188, pp. 46-53(1995); each incorporated herein by reference in their entirety.

An aerogel of the invention may comprise any material compositioncapable of forming an aerogel, as defined above. In one embodiment, theaerogel comprises a metal oxide. In another embodiment, the aerogelcomprises one or more metal oxides selected from the group consisting ofsilicon oxide, aluminum oxide, chromium oxide, titanium oxide, and tinoxide. In another embodiment, the aerogel comprises silicon oxide. In afurther embodiment, the aerogel comprises at least 95% silicon oxide bymass.

An aerogel of the invention has no particular density, as the densitywill vary depending on the aerogel's chemical composition and thefraction of its volume occupied by a gas. In one embodiment, the densityof the aerogel is between about 1 and about 500 kg/m³. In anotherembodiment, the density of the aerogel is between about 3 and about 400kg/m³. In another embodiment, the density of the aerogel is betweenabout 5 and about 100 kg/m³.

An aerogel of the invention has no particular restriction on thefraction of its volume that is occupied by a gas. In one embodiment, theaerogel is more than about 50% gas by volume. In another embodiment, theaerogel is more than about 70% gas by volume. In another embodiment, theaerogel is more than about 85% gas by volume. In another embodiment, theaerogel is more than about 90% gas by volume. In another embodiment, theaerogel is more than about 95% gas by volume. In another embodiment, theaerogel is more than about 97% gas by volume.

An aerogel-based layer of the invention may have any thickness less thanabout 1 mm. In one embodiment, the aerogel-based layer has a thicknessbetween about 100 nm and about 1 mm. In another embodiment, theaerogel-based layer has a thickness between about 500 nm and about 750μm. In another embodiment, the aerogel-based layer has a thicknessbetween about 1 μm and about 600 μm.

A writing process of the invention includes the use of any ablationmethods known to those of skill in the art except for those methodswhose use would result in structural failure of the aerogel-based layer.In one embodiment, the ablation method comprises the use of at least onetechnique selected from the group consisting of focused ion-beamwriting, plasma etching, laser ablation, reactive ion etching, and otherlike dry etching techniques. In one embodiment, the ablation methodcomprises the use of focused ion-beam writing, where the focused ionbeam apparatus is equipped with an electron shower. See C. A. Volkert &A. M. Minor, MRS Bulletin, Vol. 32, pp. 389-95 (2007); W. J.Moberly-Chan et al., MRS Bulletin, Vol. 32, pp. 424-32 (2007); J. Mayer,et al., MRS Bulletin, Vol. 32, pp. 400-07 (2007); each incorporatedherein by reference.

In one embodiment, writing occurs through a single-step process whereinan aerogel-based layer is subjected to an energy source which ablatesmatter from the aerogel-based layer to form a structural feature havinga surface contour that is substantially the same as a surface contour ofat least a part of a microelectromechanical feature.

In another embodiment, writing occurs through a two-step process. In afirst step, an aerogel-based layer is subjected to an energy sourcewhich ablates matter from the aerogel-based layer to form a firststructural feature. In a second step, matter is deposited into or ontothe first structural feature to form second structural feature, whereinthe volume of matter deposited in the second step is less than thevolume of matter ablated in the first step, and wherein the secondstructural feature has a surface contour that is substantially the sameas a surface contour of at least a part of a microelectromechanicalfeature. In other embodiments, writing may occur through single-step ormulti-step processes.

In some embodiments, an aerogel-based layer lies directly over asubstrate and the writing step ablates the aerogel-based layer so as toexpose a portion of the surface of the underlying substrate, as shown,for example, in FIG. 2. In other embodiments, an aerogel-based layerlies directly over a substrate and the writing step ablates theaerogel-based layer so as not to expose a portion of the surface of theunderlying substrate. In yet other embodiments, additional layers maylie between the aerogel-based layer and the substrate. In theseembodiments, the writing step at least ablates matter from theaerogel-based layer (either exposing or not exposing a surface portionof the underlying layer), but may also ablate matter from the layer(s)lying between the substrate and the aerogel-based layer (either exposingor not exposing a portion of the surface of the substrate).

A microelectromechanical feature of the invention is not limited to anyparticular type of feature, so long as it is encompassed by the abovedefinition. For a single-feature microelectromechanical apparatus, themicroelectromechanical feature may constitute the entiremicroelectromechanical apparatus. For a multiple-featuremicroelectromechanical apparatus, the microelectromechanical featureconstitutes merely part of the microelectromechanical apparatus. In oneembodiment, the microelectromechanical feature is physically and/orelectrically isolated from any other microelectromechanical feature orapparatus; for example, a grating. In another embodiment, themicroelectromechanical feature is physically and/or electricallyconnected to another microelectromechanical feature or apparatus, or anyother apparatus; for example, a fluid mixer that is connected to a flowchannel.

In one embodiment, the microelectromechanical apparatus is a fluidmixer. In another embodiment, the microelectromechanical apparatus is agrating. In another embodiment, the microelectromechanical apparatus isa flexing diaphragm.

A depositing process of the invention includes the use of any method offorming a material layer onto a surface, except to exclude techniquesthat would result in non-trivial degradation of the aerogel-based layer,or that would result in the structural failure of the aerogel-basedlayer. The depositing process may consist of a single step or multiplesteps.

In one embodiment, the depositing process comprises the use of at leastone technique selected from the group consisting of chemical vapordeposition, sputtering, evaporation, and low-pressure chemical vapordeposition.

A dense material layer of the invention comprises a material that isless than about 50% gas by volume. In one embodiment, the dense materialcomprises a material that is less than about 40% gas by volume. Inanother embodiment, the dense material comprises a material that is lessthan about 35% gas by volume. In another embodiment, the dense materialcomprises a material that is less than about 32% gas by volume.

A dense material layer of the invention is not restricted to anyparticular chemical composition, so long as the composition is suitablefor use in a microelectromechanical feature. In one embodiment, thedense material layer comprises a material selected from the groupconsisting of silicon dioxide, gold, platinum, and poly-silicon.

In one embodiment, the dense material layer has an average density thatis about 20% greater than the average density of the aerogel-basedlayer. In another embodiment, the dense material layer has an averagedensity that is about 35% greater than the average density of theaerogel-based layer. In another embodiment, the dense material layer hasan average density that is about 50% greater than the average density ofthe aerogel-based layer. In another embodiment, the dense material layerhas an average density that is about double the average density of theaerogel-based layer. In another embodiment, the dense material layer hasan average density that is about triple the average density of theaerogel-based layer. In another embodiment, the dense material layer hasan average density that is about five times the average density of theaerogel-based layer. In another embodiment, the dense material layer hasan average density that is about ten times the average density of theaerogel-based layer. In another embodiment, the dense material layer hasan average density that is about 25 times the average density of theaerogel-based layer. In another embodiment, the dense material layer hasan average density that is about 50 times the average density of theaerogel-based layer.

The deposition of the dense material layer need not directly follow thewriting of a structural feature into an aerogel-based layer. In oneembodiment, the writing of a structural feature into an aerogel-basedlayer is followed by a process or series of processes that prepares thepatterned aerogel-based layer for the depositing of a dense materiallayer. For example, the aerogel-based layer may be subjected to anysurface preparation technique known to those of skill in the art as longas the surface preparation would not result in the structural failure ofthe aerogel-based layer. In some embodiments, however, the depositing ofa dense material layer directly follows the writing of a structuralfeature into an aerogel-based layer.

A removing process of the invention includes any technique suitable forstripping away the aerogel-based layer excluding techniques that wouldresult in non-trivial degradation of any dense material layers depositedover the aerogel-based layer. In one embodiment, the removing processcomprises exposing the aerogel-based layer to at least one agentselected from the group consisting of water, an aqueous etchant, and agaseous etchant.

One aspect of the invention is directed to an aerogel-based mold usefulin the fabrication of at least part of a microelectromechanical feature.This aspect of the invention includes an aerogel-based layer depositedonto a substrate, wherein the aerogel layer has a thickness of less thanabout 1 mm, and comprises a structural feature having a surface contourthat is substantially the same as a surface contour of at least a partof a microelectromechanical feature.

FIG. 1 depicts one embodiment of this aspect of the invention. Anaerogel-based layer 11 has been formed on a substrate 10, and an outlineof a MEMS-scale cavity 12 has been patterned directly into theaerogel-based layer.

Another aspect of the invention is directed to a method of forming anaerogel-based mold useful in the fabrication of at least part of amicroelectromechanical feature. The method includes (a) providing asubstrate having an aerogel-based layer thereon, wherein theaerogel-based layer has a thickness less than about 1 mm; and (b)writing a structural feature into the aerogel-based layer, wherein thestructural feature has a surface contour that is substantially the sameas a surface contour of at least a part of a microelectromechanicalfeature.

FIG. 2 depicts one embodiment of this aspect of the invention. Anaerogel-based layer 21 has been formed on a substrate 20. A focusedgallium ion beam 23 coupled with an electron shower 24 is used to ablatematter from the aerogel-based layer 21 to form an outline of aMEMS-scale cavity 22.

Another aspect of the invention is directed to a method of fabricatingat least a part of a microelectromechanical feature. The method includes(a) providing a substrate having an aerogel-based layer thereon, whereinthe aerogel-based layer has a thickness less than about 1 mm; (b)creating a structural feature in the aerogel-based layer, wherein thestructural feature has a surface contour that is substantially the sameas a surface contour of at least a part of a microelectromechanicalfeature; and (c) depositing a dense material layer over theaerogel-based layer to form at least part of a microelectromechanicalfeature.

FIG. 3 depicts one embodiment of this aspect of the invention. Anaerogel-based layer 31 has been deposited onto a substrate 30. Anoutline of a MEMS-scale cavity 32 has been written into theaerogel-based layer 31, and a dense material layer 34 has been depositedover the aerogel-based layer 31.

The embodiments depicted in FIGS. 1-3 are offered for illustrativepurposes only. The figures are not intended to be a source of anydefinitions of terms used in the claims, and are also not intended tolimit the scope of claim terms in any manner. Furthermore, the relativescale of various elements of each figure are selected for ease ofpresentation, and may or may not be indicative of the relative scale ofthose same elements in actual embodiments of the claimed invention.

What is claimed is:
 1. A method of fabricating a microelectromechanicalstructure, the method comprising: providing a substrate having anaerogel-based layer over a portion of the substrate, the aerogel-basedlayer comprising an aerogel that is at least about 85% gas by volume;writing a structural feature in the aerogel-based layer, the structuralfeature having a surface contour that is substantially the same as asurface contour of at least a part of a microelectromechanical feature;depositing a dense material layer over the aerogel-based layer to format least part of the microelectromechanical feature, wherein a portionof the dense material layer is directly attached to another portion ofthe substrate; and removing the aerogel-based layer.
 2. The method ofclaim 1, wherein the aerogel-based layer comprises one or more metaloxides selected from the group consisting of silicon oxide, aluminumoxide, chromium oxide, titanium oxide, and tin oxide.
 3. The method ofclaim 1, wherein the aerogel-based layer comprises an aerogel that is atleast about 90% gas by volume.
 4. The method of claim 1, wherein theaerogel-based layer comprises an aerogel that is at least about 95% gasby volume.
 5. The method of claim 1, wherein the aerogel-based layer hasa thickness between about 100 nm and about 1 mm.
 6. The method of claim1, wherein the aerogel-based layer has a thickness between about 500 nmand about 750 μm.
 7. The method of claim 1, wherein the aerogel-basedlayer has a thickness between about 1 μm and about 600 μm.
 8. The methodof claim 1, wherein writing the structural feature comprises use of atleast one technique selected from the group consisting of focused ionbeam writing, plasma etching, laser ablation, and reactive ion etching.9. The method of claim 1, wherein the dense material layer comprises amaterial selected from the group consisting of silicon, silicon oxide,gold, and platinum.
 10. The method of claim 1, wherein depositing thedense material layer comprises use of at least one technique selectedfrom the group consisting of chemical vapor deposition, sputtering,evaporation, and low-pressure chemical vapor deposition.
 11. The methodof claim 1, wherein the aerogel-based layer is removed so as to leavethe dense material layer formed as at least part of the microelectromechanical feature.
 12. The method of claim 1, wherein removingthe aerogel-based layer comprises exposing the aerogel-based layer to atleast one agent selected from the group consisting of water, an aqueousetchant, and a gaseous etchant.
 13. The method of claim 1, wherein thesurface contour of the structural feature corresponds to a surfacecontour of a microelectromechanical apparatus comprising a fluid mixer,a grating, or a flexing diaphragm.
 14. A method of fabricating amicroelectromechanical structure, the method comprising: providing asubstrate having an aerogel-based layer over a portion of the substrate,wherein the aerogel-based layer comprises an aerogel that is at leastabout 90% gas by volume and having a thickness less than about 1 mm;writing a structural feature in the aerogel-based layer, the structuralfeature having a surface contour that is substantially the same as asurface contour of at least a part of a microelectromechanical feature;depositing a dense material layer over the aerogel-based layer to format least part of the microelectromechanical feature, wherein a portionof the dense material layer is directly attached to another portion ofthe substrate; and removing the aerogel-based layer.
 15. The method ofclaim 14, wherein the aerogel-based layer comprises one or more metaloxides selected from the group consisting of silicon oxide, aluminumoxide, chromium oxide, titanium oxide, and tin oxide.
 16. The method ofclaim 14, wherein a focused ion beam coupled with an electron shower isused to ablate matter from the aerogel-based layer during the writing ofthe structural feature.
 17. The method of claim 14, wherein the densematerial layer comprises a material selected from the group consistingof silicon, silicon oxide, gold, and platinum.
 18. The method of claim14, wherein depositing the dense material layer comprises use of atleast one technique selected from the group consisting of chemical vapordeposition, sputtering, evaporation, and low-pressure chemical vapordeposition.
 19. The method of claim 14, wherein the aerogel-based layeris removed so as to leave the dense material layer formed as at leastpart of the microelectromechanical feature.
 20. The method of claim 14,wherein removing the aerogel-based layer comprises exposing theaerogel-based layer to at least one agent selected from the groupconsisting of water, an aqueous etchant, and a gaseous etchant.